PHP parses binary IPTC http://www.iptc.org/ chunks into single tokens

php editor Banana shared a PHP article about parsing binary IPTC blocks into individual tags. The article explains how to use a PHP library to parse chunks of IPTC data extracted from images and convert them into individual tokens that are easy to process. This technique is useful for extracting metadata information from images, helping developers process and utilize this data more easily. The article details the parsing process and code examples, making it a valuable guide for developers interested in image processing and metadata extraction.

background

IPTC (International Press Telecommunications Commission) http://www.iptc.org/ blocks contain metadata embedded in image files that describe the image content and source. These chunks contain various tags, each representing a specific type of metadata.

Parsing IPTC blocks using PHP

To parse an IPTC block using php, you can use the following steps:

1. Read binary IPTC block:

   • Extract the binary representation of IPTC blocks from the image file.
   • This can usually be achieved by using the getimagesize() or exif_read_data() function of an imaging library (such as GD).

2. Loop through blocks:

   • Use while or for to loop through the bytes in the IPTC block.

3. Parsing tag header:

   • Read the first byte of each tag, which represents the tag identifier.
   • Parse subsequent bytes to determine the type and length of the token.

4. Read tag data:

   • According to the tag type, read the data associated with the tag.
   • The data type varies from tag to tag and can be a string , a number, or other formats.

5. Storage parsed data:

   • Store parsed metadata in key-value pairs or use properties of the object.
   • This will make the metadata easy to retrieve and use.

Sample code

The following PHP code demonstrates how to parse an IPTC block:

function parseIptcBlock($iptcBlock) {
$offset = 0;
$metadata = [];

while ($offset < strlen($iptcBlock)) {
$tagIdentifier = ord($iptcBlock[$offset ]);

if ($tagIdentifier === 0) {
break;
}

$tagType = ord($iptcBlock[$offset ]);
$tagLength = unpack("N", substr($iptcBlock, $offset, 4))[1];
$offset = 4;

switch ($tagType) {
case 2:
$metadata[$tagIdentifier] = unpack("a*", substr($iptcBlock, $offset, $tagLength))["a*"];
break;
case 3:
$metadata[$tagIdentifier] = unpack("n*", substr($iptcBlock, $offset, $tagLength))[1];
break;
case 4:
$metadata[$tagIdentifier] = unpack("V*", substr($iptcBlock, $offset, $tagLength))[1];
break;
}

$offset = $tagLength;
}

return $metadata;
}

Advanced usage

In addition to basic parsing, the following advanced techniques can also be used:

• Handling embedded IPTC blocks: Some image files may contain multiple IPTC blocks. If embedded IPTC blocks are present, they can be parsed using a recursive method.
• Use IPTC extensions: PHP has several extensions (such as IPTC parser) that provide more advanced IPTC parsing functions.
• Validate IPTC data: Parsed IPTC data should be validated using IPTC specifications to ensure its completeness and accuracy.

By following these steps and leveraging advanced techniques, you can effectively parse IPTC blocks using PHP. This will enable you to access and use valuable metadata embedded in image files.

The above is the detailed content of PHP parses binary IPTC http://www.iptc.org/ chunks into single tokens. For more information, please follow other related articles on the PHP Chinese website!